Laser Engines - Technical questions

[Ron Gray]

ah Bob, if your engine is correctly tuned then you won't get dead sticks!

[Bob Cotsford]

they're not all Lasers Ron! Come to that, not all have perfect tank setups, eg my Provost with Laser 100, that can get a bit iffy after a stall turn, spin or flick, I think it's because I couldn't get the tank low enough. OBG just makes sure they pick up again cleanly.

[Ron Gray]

Very true Bob. I've got several flying colleagues who have Saito and OS and they tend to use OBG, especially when the engines are new, mainly because they can't get a reliable tick over. To be fair some of them remove the OBG once the engines are well and truly run in. I have told them that they need to get Lasers!

Edited By Ron Gray on 01/02/2018 11:46:15

[Geoff S]

Posted by Martin Harris on 31/01/2018 23:49:24:

LASER SINGLE CYLINDER ENGINES

Laser-61, 75, 80, 90,100, 120, and 150.
The two cams are identical and interchangeable.
The inlet starts opening at approximately 40 degrees before top dead centre. (BTDC)
The exhaust finally closes at approximately 30 degrees after top dead centre. (ATDC)

The cams on my Laser 62 are certainly not identical as can be seen here:

There's a lot more dwell on the exhaust cam. I admit the photo isn't super clear but the marks (not done by me and presumably original) indicate the centre of highest lift. I assume the design changed with later engines. The followers stop the cams themselves falling out when the back plate/cam box cover is removed.

Geoff

[Chris Walby]

I am toying with the idea of "extending" the slow run needle on my 70 because I stupidly aligned it under the model at an angle with a cowl in the way (lesson learnt so won't do that again).

The slow running needle appears to be knurled with a slot in it and unfortunately for me unsighted once the engine is running and burnt fingers if its nicely warmed up!.

Three options spring to mind, but I am open to suggestions

1/ Learn to poke the screwdriver through the cowl, find the needle screw head and adjust

2/ Extend the needle to the outside of the cowl, how's that done?

3/ Attach the head of a cap head screw to the needle so if I poke a ball driver up there its easy to find and stay located for adjustment and the driver removed at all other times

I might just do nothing and tune it by stopping it between every adjustment, but it bugging me as occasionally I can hear its slightly off and it just needs a tweak to get it 100%.

Cheers chaps

[Geoff S]

Chris, can you insert a piece of (say) snake outer tubing to guide your screwdriver to the slot? It was a method used on some TV receivers to guide a trim tool to set up turret tuning in the days of VHF TV.

Geoff

[Jon H]

Chris, if you set up the slow run needle then fit the cowl the job is much easier. In general the slow run tuning wont change once the cowl is added.

Bert, 40:1 is what im targeting with 50:1 if you use the premixed aspen2.

On board glow is once of those debates that rages on and on. we dont recommend them for a number of reasons mostly related to reliability as they often snuff it or lack the required oomph to get the thing going. Worse still the 'on up to 1/4 throttle' types mast tuning errors and often cause the engine to stop as soon as the glow drops out.

From my own personal experience trying to keep multi cylinder engines from other brands going with OBG i can say that its not won any love from me. The blasted thing was always causing trouble and in the end i gave up on both it and the engine it was attached to in the end as neither was really airworthy and it just was not worth the bother.

[Martin Harris - Moderator]

Posted by Geoff Sleath on 01/02/2018 12:28:00:

Posted by Martin Harris on 31/01/2018 23:49:24:

LASER SINGLE CYLINDER ENGINES

Laser-61, 75, 80, 90,100, 120, and 150.
The two cams are identical and interchangeable.
The inlet starts opening at approximately 40 degrees before top dead centre. (BTDC)
The exhaust finally closes at approximately 30 degrees after top dead centre. (ATDC)

The cams on my Laser 62 are certainly not identical as can be seen here:

There's a lot more dwell on the exhaust cam. I admit the photo isn't super clear but the marks (not done by me and presumably original) indicate the centre of highest lift. I assume the design changed with later engines. The followers stop the cams themselves falling out when the back plate/cam box cover is removed.

Geoff

Quite right Geoff. When I rebuilt my 62 I was quite surprised that the inlet cam was seemingly lower duration than the exhaust - not something that I was familiar with from my car and motorcycle engine experience. I did edit Neil's document which specifically mentions this point for the older range of engines.

[Ron Gray]

@Chris - another suggestion is to use heat shrink as you can shrink it onto the head of the adjuster and run it out to a hole in the cowl.

[Jon H]

Just a quickie on the cams. The 45, 50, 62 and 70 all have our high lift cam on the inlet. This was introduced with the 45 as it gave greater lift and greater fuel draw due to the shorter duration. It was also tested on the 120 and while performance was slightly improved we were concerned about coil binding on the valve spring due to the higher ratio rocker so did not fit it in the interest of reliability.

[Chris Walby]

Thanks Geoff, Jon and Ron for your advice, I'll try the sleeve on the needle for starters to see if that works. As Jon says it should not need changing too often, but it will be nice not to stop/tweak/start it each time.

Plus next time install the engine so I can get to it !

[Ron Gray]

And there was me thinking that the and there was me thinking that the 160v problems had been resolved by the replacement of the on board glow drivers with use of standard glow sticks. I took the WWXL up to the field and it started straight away so after a warm up I taxied out and took off only to have one cylinder die on me. I aborted the take off and landed, taxied back whereupon the cylinder fired up again. Thinking that the taxiing out had allowed one pot to cool, this time I held it at the end of the runway and ran it up to full throttle just to make sure it was warm. Throttled back to normal take off, both pots firing nicely but on climb out one cut out again but this time I didn’t abort I kept on going but found that if I dipped the nose the dead pot would fire up again but cut out as soon as the nose was lifted. So completed one circuit and landed and both cylinders firing on taxi back to the pits. It occurred to me that the engine must be leaning out so to test this theory I ran the engine up in the pits and raised the WW’s nose and sure enough one pot cut out but reignited when I lowered the nose. So I slightly increased the richness (on both cylinders as I couldn’t be sure which one was playing up). Took off again and this time was able to climb out with both pots firing. I did find that on verticals, it was again losing one pot but I was ok with that so continued to have some flying fun. After an 8 minute flight I came in to land and on approach lost a pot. Trying to get it started again after it had cooled down was a right pain but did get it going, so out I went again only for it to lose a pot on take off which I then aborted.

Feeling extremely frustrated I decided to strip out the motor and fuel tank and in doing so I noticed that one on the in-line filter bodies wasn’t fully done up and this could be letting air in. Now I had been running with these filters in place from day 1 but on advise from you guys I was going to remove them but as the fuel tube wouldn’t then be long enough, all I did was remove the filter element from within the bodies and leave the empty bodies in place. With the tank out I was now able to replace the tubing. To prove my theory that air leaking was the problem, I built a test rig and put the engine and replumbed tank on it and fired it up, readjusting the richness back to ‘normal’. This time when I tilted the rig there was no drop out from either cylinder. Back up the field last week I completed 5 8 minute flights with no issues. Job done!

[Former Member]

[This posting has been removed]

[cymaz]

well done Ron

[Ron Gray]

I’ll still keep them in place on my gassers, but all my glow ‘planes have now had fuel filters removed. I do have one in the bottle plus another on the feed line to the tank, but nothing on board anymore. Lesson learnt.

[ASH.]

Never had a problem with Sullivan inline fuel filters. The filter has 2
gauzes and is see through - it works perfectly.

[Jon H]

We don't recommend the use of fuel filters on models for the various reasons described here.

In general it is a better practice to filter the fuel before you put it in the model.

My own setup is to use a fairly course filter as the pickup from my fuel bottle and then one of the really fine filters the jet boys use on the outlet of the pump. I have done things this way for many years and never suffered from any issues.

Our petrol engine however will be a different animal and each engine will come with a filter installed just before the carburettor. This is to catch any small fibres that can come off of felt clunks over time. The felt clunk is there mostly to prevent bubbles getting into the system as bubbles are not something you want in a pumped system

[bert baker]

What make of carb will be on the petrol Lasers

[cymaz]

Walbro I wonder hope Good reliability, spares and servicing a doddle

[Don Fry]

Seem to remember, it a Laser design. But senile dementia is coming faster than the production engine.

[Engine Doctor]

Have you tried Sintered Metal clunk filters? They are a brilliant filter cant leak air like inline filters and have vast filter area unlike the inline type that can easily become clogged , leak air and filter gauze deteriorate and break down if any nitro fuel is used. They also work well with petrol and don't dry out or go hard like some felt filters . I also use them on the filling pump so fuel is pre-filtered before even getting into the models tank.

[Jon H]

Posted by Engine Doctor on 11/02/2018 20:25:31:

Have you tried Sintered Metal clunk filters? They are a brilliant filter cant leak air like inline filters and have vast filter area unlike the inline type that can easily become clogged , leak air and filter gauze deteriorate and break down if any nitro fuel is used. They also work well with petrol and don't dry out or go hard like some felt filters . I also use them on the filling pump so fuel is pre-filtered before even getting into the models tank.

I have not tested them. As I'm sure you can imagine trying to test every combination of accessories available is virtually impossible so we have gone for the simple route of following the crowd and recommending a felt clunk. I don't expect that a sintered jobby would be any problem though.

[Jon H]

Posted by cymaz on 11/02/2018 17:39:03:

 

 

Walbro I wonder hope Good reliability, spares and servicing a doddle

 

having tested about 20 different types I concluded that they were too inaccurate and too fussy. I gave up on them and designed my own using a fully mechanical system without reliance on air pressure for fuel regulation.

Performance vs the diaphragm regulated types was immediately superior so I abandoned them and went another route. The result is easier to set up, maintenance free as well as being smaller, lighter, and having better performance.

Edited By Jon Harper - Laser Engines on 11/02/2018 20:40:03

[onetenor]

Jon if you can't supply st carb parts can you give dimensions to see if they can be sourced elsewhere. Thanks for all your advice.

Edited By Steve Hargreaves - Moderator on 25/02/2018 18:06:18

[Jon H]

We stopped using these carbs in 1995 and ST engines themselves completely disappeared probably 8-10 years ago. Spares are rare as rocking horse poop and we are no longer able to supply anything for them. The only person who might be able to help is Dave at Motors and Rotors.

In the event that you find yourself with a dead ST carb we can supply a new carb for your engine assuming it was manufactured after 1992. Before that our current carb wont fit.

Edited By Steve Hargreaves - Moderator on 25/02/2018 18:06:42